Antagonism of teicoplanin and vancomycin activity by chocolatized Mueller-Hinton agar

Chocolatized (80 degrees C, 13 min) Mueller-Hinton agar antagonized the inhibitory activities of teicoplanin and vancomycin against reference strains of Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, Staphylococcus aureus, and Enterococcus faecalis. This antagonism was due to heat-exposed sheep erythrocytes, sheep hemoglobin, and the supernatant fluid from lysed sheep erythrocytes, but not to sheep serum. Neither water-soluble cholesterol, bovine albumin, bovine serum, hematin, hemin nor egg yolk suspension antagonized teicoplanin and vancomycin.